1. Field of the Invention
The present invention relates to an apparatus for forming a thin film and, more particularly, to an apparatus which is suitable for use in forming a thin film on a substrate in a semiconductor production system.
2. Description of the Related Art
FIG. 3 shows a known thin-film forming apparatus of vapor chemical reaction type relying upon a plasma excitation. This apparatus has a reaction chamber 3 and a heating plate 2 disposed at the center of the reaction chamber 3. The apparatus also has a material gas supplying section 4 and an activated gas supplying section 7 disposed on one side of the reaction chamber 3. The material gas supplying section 4 is capable of supplying into the reaction chamber 3 a material gas G.sub.1 containing components of the thin film to be formed on the surface of a substrate 1. For instance, when a thin film of a silicon compound is to be formed, a silane gas is used as the material gas G.sub.1. On the other hand, the activated gas supplying section 7 is adapted for supplying into the reaction chamber 3 a reaction gas G.sub.2 such as N.sub.2, O.sub.2 or the like activated by a plasma. A plasma generating section 5 is connected to the activated gas supplying section 7 through an activated gas introduction pipe 6. An evacuating section 8 is connected to the reaction chamber 3.
The operation of this apparatus will be described on an assumption that a nitride film is to be formed as the thin film. Substrates 1 are placed on a heating plate 2. The heating plate 2 is supplied with power to generate heat, thereby heating the substrates 1 up to, for example, 300.degree. C. Meanwhile, N.sub.2 gas is supplied to the plasma generating section 5, as the reaction gas G.sub.2. The reaction gas G.sub.2 is activated by the plasma, and then supplied into the reaction chamber 3 through the activated gas introduction pipe 6 and the activated gas supplying section 7. At the same time, silane gas as the material gas G.sub.1 is supplied into the reaction chamber 3 through the material gas supplying section 4. In the reaction chamber 3, the material gas G.sub.1 and the reaction gas G.sub.2 react to form a thin film of silicon nitride on the surface of the substrate 1. The gases in the reaction chamber 3 are discharged through the evacuating section 8 so that a substantially constant pressure of, for example, 0.1 Torr is maintained in the reaction chamber 3.
This known apparatus, however, suffers from the following problems.
Namely, since the reaction gas G.sub.2 activated by the plasma in the plasma generating section 5 flows a long distance to the reaction chamber 3 through the activated gas introduction pipe 6, the activity possessed by the reaction gas G.sub.2 is seriously wasted during flowing of the gas. In addition, it has been difficult to uniformly supply the reaction chamber 3 with the reaction gas G.sub.2 which has been introduced from the plasma generating section 5 through the activated gas introduction pipe 6 and which enters the reaction chamber 3 through the activated gas supplying section 7. For these reasons, the known apparatus could not cope well cope with a demand for quick formation of a uniform thin film over a wide area.